1. Field of the Invention
The invention relates to a sewage lagoon system.
2. Description of Related Act
Instead of sewage treatment plants that use either trickling filters or the activated sludge process, smaller communities in rural areas often use lagoon systems for the mechanical-biological purification of their waste water, which operate with less technical expenditure, but require a larger area per inhabitant. A sufficient dimensioning being provided, it is possible to degrade the solids and the dissolved and undissolved organic carbon compounds contained in domestic sewage by means of aerated lagoons. In order to further achieve a thorough oxidation of the nitrogen compounds present in the waste water, further measures are required. Nitrogen compounds are converted by hydrolysis into ammonium and, subsequently, to nitrate by oxidation. Ammonium is a nutrient for plants, it is poisonous to fish and consumes oxygen. The nitrification, i.e. the conversion of nitrogen compounds to nitrate, is effected with the help of bacteria, the so-called nitrobacteria. In contrast to those bacteria that degrade carbon compounds, nitrobacteria grow slowly so that the sludge needed for the nitrification has to be of a comparatively high age. If the nitrification and the degradation of the carbon compounds are effected at the same time, there is the problem that the nitrobacteria are covered by the fast-growing bacteria responsible for the degradation of the carbon compounds, the nitrobacteria thus being ineffective.
It is known in activated sludge plants to install contact beds in the activated sludge tank, in which a sludge layer gathers to form old sludge. Additionally, an aeration of the activated sludge tank is provided. Such purification systems are described, e.g., in German Laid Open Patent Application 29 01 509 and in German Laid Open Patent Application 33 27 774 A1. An activated sludge plant is a highly concentrated purification system with a low area demand per inhabitant and a high degree of technicalization. The activated sludge, or a part thereof, leaving the activated sludge tank is returned into the activated sludge tank via a sludge return path, so that old sludge may form therein. Sewage works with activated sludge tanks require considerable production and maintenance expenditures. In contrast thereto, other conditions prevail in simple sewage lagoon systems.
It is known from German Laid Open Patent Application 35 22 965 A1 to arrange contact beds swimming submerged in an aerated basin or lagoon filled with waste water. These contact beds serve for the gathering of sessile biomass. Flow occurs through the contact beds horizontally.
A lagoon system is known from German Laid Open Patent Application 36 10 181 A1. This known sewage lagoon system has a clarifying pond and an adjoining nitrification lagoon. The aeration in the nitrification lagoon is effected by a compressed air aeration device arranged on the bottom of the lagoon, above which guide walls are disposed that define a vertical shaft. The buoyancy flow caused in the shaft by the ascending air effects the formation of circulations in the nitrification lagoon and, at the same time, the aeration of the sewage. A contact bed is mounted in the shaft, through which flows the ascending mixture of air and water. In this sewage lagoon system, the degradation of dissolved and undissolved organic carbon compounds and the nitrification are separated, so that the nitrobacteria are not covered to a considerable extent by other microorganisms. When the waste water leaves the clarifying pond, it is already substantially free of carbon compounds, so that the activity of the bacteria is concentrated on the nitrification in the nitrification lagoon. However, it is disadvantageous that the aeration device requires a large constructional effort and high operating costs, and that the space available for the contact bed in the narrow shaft is very limited. Further, the flow rate of the circulating flow is very low, since this circulating flow is driven only by the ascending bubbles. The nitrification effect is comparatively low with a view to the energy consumption and to the high financial input.
It is an object of the invention to provide a sewage lagoon system with a high nitrification effect at low production and operating costs.